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Schumag AG is a leading manufacturer of machines and facilities for adding value to bar material and tubes made of steel and non-ferrous metals.
Besides high-performance individual units for drawing, grinding and peeling, Schumag AG also provides linked facilities with a maximum degree of automation.
The sales distribution over the past few years has revealed a clear trend towards peeling technology – a trend which is expected to continue in the future. This is due to the much more stringent demands placed on high-quality round stock with tight tolerances and particularly with zero-defect surfaces.
The recent development in the area of peeling also reveals that the market for bright steel with large dimensions is undergoing profound change. Whereas in the past the demand for peeled bars with a diameter of greater than 200mm was extremely rare, the requirements today for round stock has rocketed due to the growing energy market.
Schumag AG has been developing and producing peeling machines for dimensions of up to 400mm for decades now. After the peeling machine generation of the PM series was successfully established on the market in 2002 for applications of up to 200mm, the recent market development with respect to peeling provided the impetus for Schumag AG to develop and position the PMH series in order to maintain and significantly expand its leadership position in the area of large-dimension peeling, too.

The New PMH Peeling Machine from Schumag AG

Large-dimension peeling within bright steel production poses great challenges. One challenge lies in the fact that difficult-to-machine materials such as stainless steels and nickel-based alloys are frequently processed. The machines of the PMH series therefore have much higher power reserves than their predecessors.
Furthermore, the input stock for large bar diameters is usually forged. This production process leads, however, to the input stock being significantly more curved and unround than is the case with rolled stock.
Usually forged bars above a diameter of 250mm are processed into bright steel on lathes. This process is inefficient in two respects. On the one hand, turning requires a machining time that is up to 10 times longer. On the other hand, considerably greater levels of chip removal are necessary during turning in order to guarantee a zero-defect surface. This is due to the impossibility of following the curve of the raw material during turning. Instead, a straight, cylindrical part is always inevitably generated (see Fig. 1).
This has also been the case with peeling machine concepts to date, as conventional peeling machines operate with rigid infeed and exit guidance systems.
The new peeling machines of the PMH series are different. Depending on customer requirements, they do not only operate according to the conventional principle using rigid guidance systems. Rather, the PMH can also adapt, if necessary, to the curve of the bar, thereby leading to minimum chip removal.

Trend towards large-dimension peeling

The operating principle behind the infeed and exit guidance systems is as follows (cf. Fig. 2):

Great demands placed on large-dimension peeling

– The infeed carriage initially clamps the bar in the centre and transports it to the peeling machine. The driven rollers of the infeed roller table as well as the driven support rollers integrated in the carriage bed assist in achieving even transport of the bar.
The infeed carriage introduces the head of the bar into the opened infeed guide.
– The infeed carriage travels back (in the direction of the bar end/infeed roller table) and clamps the bar at a distance of at least 3m to the infeed guide. The clamping here is off-centre. The clamping jaws of the infeed carriage initially travel path-controlled ("without pressure") up to contact with the bar. After this, the clamping pressure is increased evenly on both sides and maintained at a constant level in the two clamping cylinders.
– The infeed carriage pushes the bar further into the machine. The peeling process begins.
– During peeling, the centre of the process is specified by the infeed guide. Any unevenness of the bar is levelled out by the infeed carriage, as the clamping cylinders float horizontally as a unit.
– As soon as the head of the bar exits the peeling machine, the exit carriage begins to move. The speed of the exit carriage is synchronised with that of the infeed carriage before the exit carriage likewise clamps off-centre. For a brief moment, the bar is clamped both in the infeed carriage as well as in the exit carriage prior to the bar being transferred completely to the exit carriage.
– Depending on the length of the bar, the transfer between the infeed and exit carriages may be repeated a number of times.
– After exiting, the bar is transported away by the support rollers integrated in the carriage bed as well as by the rollers of the exit rolling table and then dropped onto the storage bed.

Innovative machine concept

The operating principle using an infeed carriage has other advantages over the use of an infeed unit with rollers. The fact that the bars are clamped at a fixed position in the infeed carriage successfully prevents the bar from rotating during the peeling process. This bar rotation was a frequent occurrence in conventional machines when processing forged and thus relatively inaccurate material, sometimes leading to considerable machine damage.

Operating Costs

With the new PMH in combination with the peeling technology innovations that have been achieved, the developers at Schumag focussed, among other things, on attaining an optimised concept with respect to operating costs over the entire lifecycle of the machine. The maintenance and tool-changing efforts have been significantly reduced with the PMH in comparison to the previous generation of large-dimension peeling machines. The use of wear-free clamping jaws in the clamping carriage, for example, dispenses with the need to regularly change infeed rollers. Changing such worn rollers in an infeed unit not only involves several thousand euros in material costs but also requires up to half a working shift in time, during which the machine cannot produce.

First Customer

The new PMH product already has its first customer: An important European steel processor has placed an order. Other contract negotiations are currently being completed.

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